I'm not sure if this is just a quirk of Duolingo...
I was asked to choose えも plus じ. From a grammatical/etymological point of view it would be better with え plus もじ. Especially as a precursor to learning the kanji.
They do this a lot for Japanese (I can't speak on behalf of the other languages) and just to try and catch you out. Nothing to do with grammar etc, they're just making sure you're paying attention lol =P
But that's the point, you should kow what to use. And it's more knowing the word than paying attention to the speech.
They are the same, like we say "Sheen" and "Machine" (both have the same "Sh" sound).
An exercise before this asked me to match corresponding words and gave me two variations or ways of writing "ji" - じ and a character that looked like the "chi" character (ち) but with two strokes on the upper right... what is the difference between the two?
Se supone que así tienes que ordenar los kanas. No siempre va a estar completo.